The present invention relates to a starter device for an engine. More particularly, it relates to an improvement in a reduction gear device for an internal speed reduction type starter in which an input shaft and an output shaft are arranged in a single and the same axial line.
FIG. 1 shows a conventional reduction gear device of this kind.
In FIG. 1, a reference numeral 1 designates an internal speed reduction type starter containing therein an epicyclic reduction gear 2, in which a rotary shaft 5 of the armature 4 of the a d.c. motor 3 and a rotary output shaft 7 with which a starter pinion 6 is engaged through a spline structure so as to be slidable in the axial direction, are arranged in a single and the same axial line. The d.c. motor 3 comprises a stator 8, an armature iron core 9 secured to the rotary shaft 5 and an armature winding 10 wound on the armature iron core. A spur gear 11 is formed at the front part of the rotary shaft 5 and a planet gear 12 of the epicyclic reduction gear 2 is always interlocked with the spur gear 11. A sleeve bearing 13 is fitted to a through hole 12a formed in the planet gear 12 and the sleeve bearing 13 receives therein in a freely rotatable manner a pin 15 which is attached to a flange 14 having function of an arm of the epicyclic reduction gear 2. The flange 14 is fixed to the rear end part of the rotary shaft 7 at the output side. A ring gear 16 is formed integrally with a machine frame 17 which rotatably supports the rear end part of the rotary shaft 7 through a sleeve bearing 18 fitted to a central through hole 17a. A recess 19 is formed at the rear end part of the rotary shaft 7. The recess 19 receives the front bearing part 5a of the rotary shaft 5 for the armature 4 through a sleeve bearing 20 in a freely rotatable manner. A shift lever 21 is pivotally supported by a pivotal part 21a and the shift lever 21 is engaged with the starter pinion 6 to shift the same in the axial direction. There is provided a stopper 22 which is retained in an annular groove 7a formed in the rotary shaft 7 by means of a ring 23, the stopper 22 restricting forward movement of the starter pinion 6. A front frame 24 has a through hole 25 at its front end part. A sleeve bearing 26 is fitted to the through hole 25. A bearing part 7a which is formed by finely finishing the front end part of the rotary shaft 7 is rotatably supported by the sleeve bearing 26.
The operation of the conventional device will be described. When the shift lever 21 is rotated counterclockwisely around the pivotal part 21a, as shown in the arrow mark A, the starter pinion 6 is shifted on the rotary shaft 7 in the direction of the arrow mark(on the right hand), namely the starter pinion 6 is moved forwardly until it impinges the stopper 22. Then, the pinion 6 is interlocked with a ring gear (not shown) of an engine. At the same time, the d.c. motor 3 is actuated by current conduction and a rotational force is transmitted to the epicyclic reduction gear 2 through the spur gear 11 formed in the rotary motor shaft 5. By a series of operations as above mentioned, the planet gear 12 is caused to roll on the ring gear 16 to thereby rotate the flange 14 by means of the pin 15. The rotational force is transmitted to the pinion 6 on the rotary shaft 7; thus, the engine is started through the ring gear (not shown) by the rotational force.
When the shift lever 21 is returned to a position as shown in FIG. 1, the starter pinion 6 is retracted along the rotary shaft 7 to a position as shown in the FIG. 1. Then, current conduction to the d.c. motor 3 is stopped whereby the entire device is stopped.
In the conventional starter device for an engine having the construction as above mentioned, when the epicyclic reduction gear 2 is of an enclosed structure(although it is normal for the reduction gear to have the enclosed structure when it is installed in an engine starter device), structural elements constituting a reduction gear mechanism are heated at high temperature due to mechanical friction caused during the revolution of the starter device whereby there results excessive wearing of the rotating parts.